1. Field of the Invention
This invention relates to a new process for the production of new polyisocyanate compositions containing urea and/or biuret groups, the polyisocyanate compositions obtained by this process, and their use for the production of plastics materials by the isocyanate polyaddition process, in particular the production of molded plastics materials by the reaction injection molding process.
2. Description of the Prior Art
The production of urethane-modified polyisocyanate compositions, i.e. prepolymers or semi-prepolymers containing isocyanate end groups, in particular those based on polyisocyanates or polyisocyanate mixtures of the diphenylmethane series (4,4'-diisocyanatodiphenylmethane, mixtures thereof with 2,4'- and optionally 2,2'-diisocyanatodiphenylmethane or phosgenation products of aniline/formaldehyde condensates containing higher homologues in addition to these diisocyanates) and various polyhydroxyl compounds is known (see e.g. Nos. EP-A-10 850 or 66,130: Nos. DE-OS 2,347,207, 2,404,166, 2,513,793, 2,513,796, 2,620,222, 2,622,104, 2,732,182, 2,737,338, 2,804,375, 2,810,596, 2,815,579 or 2,913,126; U.S. Pat Nos. 3,644,457, 4,055,548, 4,234,714 or 4,321,333, and GB-PS No. 1,369,334).
The processes disclosed in these prior publications are generally directed to the liquefaction of a diisocyanato diphenyl methane which is solid at room temperature, in particular 4,4'-diisocyanatodiphenylmethane, or the reduction of the tendency of polyisocyanate mixtures of the diphenylmethane series which are liquid at room temperature to undergo crystallization when stored at low temperatures.
If polyisocyanates are to be prepolymerized or semi-prepolymerized with polyols, however, it is necessary to reach certain compromises regarding the structure and molecular weight of these polyols in order to achieve a liquefying effect. Because of this, the polyhydroxyl compounds which provide the best mechanical results in polyurethane plastics prepared from the polyisocyanate compositions in many cases cannot be used for this prepolymerization or semi-prepolymerization. One main disadvantage is that the urethane groups present in the prepolymers or semi-prepolvmers have little thermal resistance compared with urea or amide groups. Consequently, if the plastics prepared from these prepolymers or semi-prepolymers contain mainly urethane groups, they generally have less favorable mechanical properties at elevated temperatures than comparable plastics in which the urethane groups or at least some of the urethane groups are replaced by urea groups.
Polyisocyanates containing urea and/or biuret bonds are also known (see e.g. "Polyurethanes", Chemistry and Technology, Part I, by Saunders and Frisch, Interscience Publishers (1962), pages 190 et seq). Thus DE-PS No. 1,215,365 teaches the preparation of relatively high molecular weight polyisocyanates having a biuret structure by the reaction of at least 3 mol of an organic diisocyanate with 1 mol of an .omega.,.omega.'-diaminopolyether having an average molecular weight of 200 to 6,000, optionally mixed with a small quantity of a corresponding .omega.,.omega.'-dihydroxy- or .omega.-hydroxy-.omega.'-aminopolyether. The preparation of liquid polyisocyanate compositions by heating an organic diisocyanate with a solution of an aromatic diamine in an organic solvent to a temperature of 150.degree.-200.degree. C. for 1-4 hours is described in GB-PS No. 1,078,390 .
A process for the preparation of biuret polyisocyanates by the reaction of at least 3 mol of a diisocyanate with 1 mol of water is described in DE-PS No. 1,101,394.
Isocyanate compositions which contain urethane groups in addition to biuret and urea groups may also be obtained by the reaction of mixtures of ketones and dior polyamines with di- or polyisocyanates in accordance with GB-PS No. 1,263,609. Suspensions of isocyanate ureas which are liquid or pasty at room temperature or can be liquefied by heating to 80.degree. C. are described in No. DE-OS 2,902,496. These isocyanate urea suspensions are prepared by mixing aromatic diisocyanates with isocyanate prepolymers and then reacting the mixture with 0.4-0.8 mol of water per mol of the aromatic diisocyanate or with a corresponding quantity of a compound which splits off water. According to No. DE-OS 1,963,190, liquid diprimary aromatic diamines whose reactivity with isocyanates has been reduced by electrophilic or sterically hindered substituents are reacted with polyisocyanates to form stable, liquid polyisocyanates containing biuret groups. According to No. DE-OS 2,010,887, mono- and polyamines containing secondary amino groups are reacted together at 80.degree.-200.degree. C. for the preparation of liquid polyisocyanates containing biuret groups. According to No. DE-OS 2,032,547, these starting components give rise to isocyanates containing urea groups which are liquid at a temperature of -20.degree. to 80.degree. C. No. DE-OS 2,261,065 describes the reaction of organic polyisocyanates with subequivalent quantities of aliphatic or cycloaliphatic diamines to form the corresponding polyisocyanates containing biuret groups. According to No. DE-OS 3,003,543,urea-modified polyisocyanates are obtained by the reaction of simple polyisocyanates with subequivalent quantities of polyamines containing more than 3 non-aromatically bound amino groups. According to No. DE-OS 3,114,638, special diisocyanates and/or diamines containing aromatically bound isocyanate or amino groups are used for the preparation of aromatic polyisocyanates containing urea and/or biuret groups. U.S. Pat. No. 3,906,019 describes the preparation of di-(isocyanatotolyl)-urea by the reaction of tolylene diisocyanate with water in excess tolulene diisocyanate. Products which have melting points in the region of 170.degree.-180.degree. C. and are extremely insoluble in tolylene diisocyanate are obtained.
The products of the processes disclosed in these prior publications have, however, not achieved any position of significance for the production of position of significance for the production of semi-rigid, foamed or unfoamed, molded elastomeric plastics of the type obtainable by the reaction injection molding technique.
It is an object of the present invention to provide a process for the production of polyisocyanate compositions containing urea and/or biuret groups which would combine the following advantages:
1. It should be possible to use water as reactant for the starting polyisocyanates in addition to other compounds containing isocyanate reactive groups.
2. Production of the polyisocyanate compositions should lead to a reduction in the tendency of the starting polyisocyanates to crystallize at room temperature, in particular when using the preferred starting polyisocyanates, i.e. polyisocyanate mixtures of the diphenylmethane series predominantly containing 4,4'-diisocyanatodiphenyl methane, or, if 4,4'-diisocyanatodiphenyl methane is used, it should lead to liquefaction of this starting diisocyanate.
3. The process should be able to be carried out in a simple manner at relatively low temperatures and have a wide range of possible variations, i.e. it should be possible to obtain liquid, storage stable polyisocyanate compositions not only by using water as a reactant, but also by reacting the organic polyisocyanates with low molecular weight, aliphatic and, in particular, also aromatic di- and/or polyamines which have previously only resulted in difficulty soluble ureas or polyureas when reacted with organic polyisocyanates.
This problem was able to be solved by the process described in more detail below, in which mixtures of water, certain relatively high molecular weight compounds containing isocyanate reactive groups, in particular amino groups, and, optionally, also certain low molecular weight compounds containing isocyanate reactive groups, in particular amino groups, are reacted with excess quantities of organic polyisocyanates to produce storage stable polyisocyanate compositions containing urea and/or biuret groups. The possibility of carrying out the process according to the invention is surprising in that it is known that water reacts with organic polyisocyanates to form difficulty soluble ureas and polyureas.